1. Field of the Invention
The present invention generally relates to an image acquiring technology and, more particularly, to an apparatus and a method for image calibration and an apparatus for image acquiring.
2. Description of the Prior Art
A white-light interferometric system cannot be used for performing lateral measurement and defect detection because interference fringes appear in the image formed at the objective focal point due to the interferometric configuration.
To overcome such a problem, U.S. Pat. No. 7,068,376 discloses an interferometric system as shown in FIG. 1. The optical interferometric system 1 comprises a light source 10, a beam splitting unit 11, an interferometric unit 12 and an image acquiring unit 13. The light source 10 generates a light beam, which becomes a collimated light beam after it passes a collimator lens 14. The collimated light beam is reflected by the beam splitting unit 11 to the interferometric unit 12 and thus becomes a measurement light beam and a reference light beam. The measurement light beam is incident on an object to be tested 100 and is reflected thereby back to the interferometric unit 12. Then the measurement light beam is interfered by the reference light beam to form an interfered light beam. The interfered light beam is received by the image acquiring unit 13 after it passes the beam splitting unit 11 so as to form an image with interference fringes.
In the aforementioned prior art, a phase shift method is used to calculate the three-dimensional profile of an object to be tested. Combined operation is performed on a sequence of images acquired by the phase shift method so as to obtain the direct-current (DC) component of the images. The obtained images are free of interference fringes and are used for two-dimensional lateral detection. However, the two-dimensional fringeless images are obtained after the phase shift process, which causes limited imaging range and wastes longer time.